Characteristics of new particle formation events in Nanjing, China: Effect of water-soluble ions

• The characteristics of NPF events are examined in the YRD region.
• Aerosol size distributions from 10 nm to 10 μm are measured in Nanjing.
• The water-soluble ions of aerosol from 10 nm to 18 μm are determined in Nanjing.
• Interaction mechanisms between NPF events and water-soluble ions are investigated.

New particle formation (NPF) events and water-soluble ions were studied at the meteorological building on the campus of the Nanjing University of Information Science and Technology (NUIST), which is located in the western part of the Yangtze River Delta (YRD). A wide-range particle spectrometer (WPS) provided particle number size distributions between 10 nm and 10 μm, whereas water-soluble ions for particles with diameters between 10 nm and 18 μm were measured using a 13-stage Nano-MOUDI aerosol sampler and 850 professional Ion Chromatography (IC). Additionally, meteorological data, trace gas concentrations and mass concentration were recorded. Ten NPF days were captured during the measurement period from 08 July to 02 August 2012. The mean aerosol number concentration, which was primarily composed of Aitken-mode particles, i.e., with diameters of 20–100 nm, was 13,664 cm−3, which was 1.9 times larger than that on non-NPF days. The results suggest that the NPF events were only slightly affected by O3, SO2, and NO2; the primary factors affecting NPF events were meteorological factors and air mass directions. NPF events were found to be favorable during the summer in the presence of high temperatures, strong radiation, low humidity, strong winds and clean air masses originating from the southeastern coast. The mean growth rate (GR), formation rate (J10), condensational sink (CS), condensing vapor rate (Q), and condensation vapor (C) were determined to be 7.6 nm h−1, 3.7 cm−3 s−1, 2.8 × 10−2 s−1, 2.9 × 106 cm−3 s−1, and 10.5 × 107 cm−3, respectively, on NPF days. The largest effects of the studied NPF events were on the mass and water-soluble ion concentrations of Aitken-mode particles, followed by nuclei-mode particles; few contributions to accumulation- and coarse-mode particles were observed. Different water-soluble ions were observed to have distinct interactions with the NPF events. The proportions of NH4+, SO42−, NO3−, K+ and Mg2+ in nuclei- and Aitken-mode particles to the total concentrations on NPF days were substantially higher than on non-NPF days.